1. Field of the Invention
The present invention relates to an apparatus and method for detecting a preamble packet in an orthogonal frequency-division multiplexing (OFDM) system; and, more particularly, to an apparatus and method for detecting a preamble packet using a final cross-correlation value calculated by calculating a cross-correlation value between a received signal and previously stored preamble pattern values for an OFDM symbol region (N-point), delaying the calculate cross-correlation value as long as a M-point interval, measuring a receiving power for a guard interval, and calculating the final cross-correlation value by dividing the delayed cross correlation value by the measured power.
This work was supported by the Information Technology (IT) research and development program of the Korean Ministry of Information and Communication (MIC) and/or the Korean Institute for Information Technology Advancement (IITA) [2006-S-071-01, “Development of UWB Solution for High Speed Multimedia Transmission”].
2. Description of Related Art
If a transmitter transmits a signal having a preamble packet as the first step of synchronization in an orthogonal frequency-division multiplexing (OFDM) system, the transmitted signal is influenced by noise or multipath environment. If an interference signal exists, a receiver receives the transmitted signal with the interference signal. The receiver determines whether the received signal is a preamble packet signal or not by determining whether the preamble packet is included in the received signal or not.
Such a packet detecting performance depends on how accurately detect an OFDM signal using a received signal which is influenced by noise or multipath environment.
Many conventional methods for detecting a preamble packet in an OFDM system have been introduced. For example, a preamble packet is detected by measuring the power of a received signal or by detecting a preamble pattern of a received signal.
In the conventional method for detecting a preamble packet by measuring the power of a received signal, if a preamble packet is not transmitted from a transmitter, a received signal includes only noises. If a preamble packet is transmitted, a received signal includes a preamble. Therefore, if the received signal includes a preamble, the received signal must have higher energy. That is, the signal energy is zero in a period with only noises, and the signal energy increases in a period of receiving a preamble. A preamble packet can be detected by detecting the increment of signal energy.
In a conventional preamble pattern detecting method, a preamble packet is detected based on whether a predetermined preamble pattern is detected or not in a receiver because the predetermined preamble pattern exists in an OFDM system. That is, a receiver detects a preamble packet by calculating a correlation between a predetermined preamble pattern and a received signal.
However, it is impossible to accurately detect a preamble packet in noise or multipath environment using the conventional packet detecting methods.